Method of making encased magnetic core



J. cooK 3,324,532

y June 13, 1967 l METHOD OF MAKING ENCASED MAGNETIC CORE originan Filedsept. 14, 1960 W17' figa l l E 8 gj.. 16.5 210. 11 1o l 14 157i /eg Q9Mm 0 1B 10B 50 U 'fm 60 1611 l!!! 321% [245 Q 66B m- Et I 65B E0 l 16 1mil', n mi ffl .6. MB 66B y s" I n v M \44//1 mi 415/; m 161 l' INVENTOF1M PLV Q.

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Z'G Bt; ATTORNEYS 3,324,532 METHOD F MAKING ENCASED MAGNETIC CORE .lohnW. Cook, Shady Side, Md., assignor, by mesne assignments, to SpragueElectric Company, a corporation of Massachusetts Original applicationSept. 14, 1960, Ser. No. 55,890. Di-

vvided and this application June 8, 1965, Ser. No.

1 Claim. (Cl. 29-155.56)

vThis is a division of application Ser. No. 55,890 filed Sept. 14, 1960,and now abandoned.

This invention relates to encasing toroidal magnetic cores of thesmaller variety known as bobbin cores, and it more particularly relatesto enclosing bobbin cores in a tube on which the core is wound.

.The tape used in bobbin vmagnetic cores is extremely thin, fragile andstrain-sensitive being only a fraction of a mil in thickness. It iswound upon bobbins which must be resistant to high temperatures in theneighborhood of 1000 C.`because the tape must be annealed at thesetemperatures after winding to adjust its magnetic properties to optimumvalues. These bobbins have, therefore, usually been made of ceramicmaterial which is an effective insulator as well as being resistant tothe high annealing temperatures. After annealing, the tape has beensealed within the flanges of the bo-bbin, for example, by wrapping anadherent tape about the periphery of the flanges. ExtremeV care must betaken in this enclosing 'process or` any other -that is yconducted afterannealing because any stress transmitted to the tape no matter howslight will disturb the critical adjustment of its magnetic propertiesaccomplished during annealing.

An object of this invention is to provide a method of encasing a-bobbin-type core which minimizes the transmission of forces to the coreafter annealing.

Another object is to provide such a method of encasing cores withmaterials whi-ch are resistant to heat thereby permitting enclosure ofthe core prior to annealmg.

In accordance with this invention a hollow toroidal shell formedentirely of material of tubular structure is enclosed around a magneticcore. The formed shell extends radially outwardly from both ends of thetubular structure -and substantially laterally parallel to it from atleast one end. These extensions formed from both endsextend closelyadjacent each other to substantially enclose a magnetic winding disposedabout the tubular structure within the shell, and the adjacent ends ofthe shell are joined by a sealing means to tightly seal the windingwithin the shell.

Novel features and advantages of the present invention will becomeapparent to one skilled in the art from a reading of the followingdescription in conjunction with the accompanying drawings whereinsimilar reference characters refer to similar parts and in which:

FIGURE 1 is a View in elevation of one embodiment of this invention;

FIGURES 2-5 are cross-sectional views in elevation of the embodimentshown in FIGURE l throughout successive stages of fabrication;

FIGURES 6-9 are cross-sectional views in elevation of another embodimentof this invention throughout the successive stages of fabrication;

FIGURE 10 is a cross-sectional view in elevation of still -anotherembodiment of this invention; and

FIGURE l1 is a cross-sectional view in elevation of a further embodimentof this invention.

In FIGURES 1-5 is shown an encased magnetic core 10, which includes atoroidal casing 12, formed entirely of material of tubular structure 14as indicated by its initial tubular form shown in FIGURE 2. The materialof tubular structure 14 is, for example, a heat-resistantnonferromagnetic material such as stainless steel which is extremelystrong and resistant to high annealing tem- .peratures A magneticwinding 16 made, for example,

of thin magnetic tape 0.000125 inch thick is wound about tubularstructure 14.

FIGURE 3 shows how a forming die 18 is utilized to deform the ends oftubular structure 14 radially outwardly and then substantially laterallyparallel as indicated in the lower portion of FIGURE 3 which has beenformed in this manner to provide one half 20 of toroidal shell 12. Afterthe forming operation indicated in FIG- URE 3 is completed, the twohalves 20 of toroidal shell 12 substantially enclose tape winding 16within it. The ends 22 extending from both ends oftubular structure 14are spaced a slight distance from each other to break the electricalcircuit about the shell. Since shell 12 is made of heat-resistantstainless steel, it can be exposed to high annealing temperaturesvwithout destroying it.

After annealing, the opening into enclosure 12 is sealed by a materialwhich is insulating such as a cement 25 or tape. A suitable cement is apolymerizing organic material such as an epoxy resin, and various typesof Iadherent types of tape, such as plastic, may be used. The veryslight separation or spacing 24 between ends 22 minimizes the strengthrequirements of the sealing material, and sealing substances which larerelatively fluid during application can therefore be dependablyutilized.

FIGURES 6-9 illustrate :another embodiment of this invention in whichthe tubular structure is composed of two cooperating portions 14A and14A-1. This pair of tubular structures 14A and 14A-1 respectively haveradial and substantially lateral and parallel extensions 20A and 20A-1to form the shell 12A shown in FIGURES 8 and 9. These tubular structures14A and 14A-1 are formed, for example, of a nonferromagnetic materialsuch as the aforementioned stainless steel which is formed in thepreviously described manner, or they may be fabricated of molded or castmaterial, such as, a heat-resistant die cast alloy.

In FIGURE 7 a magnetic winding 16A is shown wound about tubularstructure 14A. This magnetic winding 16A is, for example, an ultrafinemagnetic wire which is, for example, either a round lwire having adiameter of approximately 0.003 inch, or similar wire subsequentlyflattened to provide dimensions, of approximately 0.003 by 0.003 inch.The utilization of wire instead of tape facilitates winding within apartially enclosed structure, and it unexpectedly permits the windingoperation to be made completely automatic because wires can be providedin substantially great lengths in contrast with tape which can only behandled in limited lengths. Furthermore, Wire can be manipulatedautomatically without damage, which is practically impossible with tapewhich must be carefully manipulated by hand to avoid tearing orcreasing. Furthermore, wire can exhibit satisfactory magnetic propertiesin a core in spite of the previously widelyaccepted theory that opposingfields `would be set up which would interfere with its proper operationin a magnetic core. In fabrication, both ends of the wire would bewelded to the core before and after it is wound to secure it in place.

FIGURE 8 shows how tubular structure 14A-1 is forced into engagementwithin tubular structure 14A to provide an extremely rigid casing formagnetic winding 16A. Tubular structures 14A and 14A-1 may be formedwith great precision to dimensions which provide an intimate engagementbetween them when engaged in the manner shown in FIGURE 8. When bothtubular structures 14A and 14A-1 made of a heat-resistant material suchas stainless steel, the enclosed core 12A shown 1?` in FIGURE 8 can beannealed and then sealed `by cement 25A as shown in FIGURE 9. Anothercement seal 26A seals the opposite ends of tubular structures 14A and14A-1 if necessary. However, it is possible to make only one tubularhalf such as 14A of heat-resistant material lwhich can withstand theannealing temperature, and then subsequently enclose the core afterannealing by insertion within it of a tubular structure 14A-1 which ismade of a material such as plastic which cannot withstand annealingtemperatures.

This situation is shown in FIGURE 10 where casing half 14B-1 is made ofa strong moldable plastic such as polystyrene which is inserted within astainless steel tubular structure 14B to bring its ends 22B-1 into closeproximity to ends 22B of structure 14B. Since structure 14B-1 is made ofa nonconductive material, it can be brought directly into contact withtubularv structure 14B `with no space between ends 22B-1 and 22B. Thisfurther facilitates their joinder by cement 25B. Another cement seal 26Bis also applied to the unformed end 28B-1 of tubular structure 14B-1 toinsure that there is no break in the closure if necessary. Even thoughtubular structure 14B-1 is applied after winding 16B is annealed, thereis no undue danger of damaging the magnetic characteristics of thewinding, since itis` protected by the extended end 20B which partiallyencloses it; and the application of plastic tubular structure 14B-1 isnot likely to induce any troublesome stresses and strains in the/farstronger tubular structure 14B of stainless steel.

FIGURE 11 illustrates a toroidal shell 22C made of a heat-resistanttubular structure 14C of stainless steel upon which a winding 16C ofmagnetic `wire is wound. Tubular structure 14C is U-shaped in crosssection, and cooperating tubular structure 14C-1 which is., for example,made of plastic similar to 14B-1, therefore, need only include aradially extending ange 30C whose end 4 22C-1 contacts end 22C oftubular structure 14C. Cement seals 25C and 26C fully seal toroidalshell 22C by application to both mating ends of tubular structures 14Cand 14C-1.

What is claimed is:

A method for encasing an ultra-tine magnetic winding comprising thesteps of applying said winding about a tube of refractory `ductilemetal, forming both ends of said tube into a curved shape extendingtoward the other end of said tube and about the periphery of saidmagnetc winding and spaced apart to form a narrow separav tion to form atoroidal shell of said tube which encloses without touching the.magnetic Winding, heating the enclosed magnetic winding within thetoroidal shell, adjusting the magnetic properties of the winding byannealing, and applying a non-conducting sealing material to saidseparation in the fluid state to tightly enclose said mag netic winding.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, PrimaryExaminer.

R. W. CHURCH, I. CLINE, Assslam Examiners.

